Four steps could put an end to this history of automotive malfeasance: The government must investigate the extent of the cheating, punish VW, prosecute company officials wherever criminal behavior is found — and overhaul its system for testing vehicles’ emissions and fuel efficiency.

Right now, companies conduct tests for fuel efficiency as well as smog and soot emissions — which cause and exacerbate lung disease and worsen childhood asthma — largely on their own. With little spot-checking, the government accepts the results. But the polluters have proved they cannot be trusted to police themselves. The Environmental Protection Agency must take complete control of the tests.

Since the 1970s, company after company has been caught cheating. Chrysler recalled roughly half its 1973 vehicles after the EPA caught it using “defeat devices” that increased smog-causing nitrogen oxide emissions. General Motors paid a $45 million penalty for using devices that let 1991 Cadillacs spew three times the carbon monoxide allowed by law. Honda paid a $267 million fine for using defeat devices on 1.6 million 1996 and 1997 models. Diesel engine manufacturers were fined more than $1 billion in the 1990s for using similar devices.

Last year, Hyundai and Kia were fined for overstating their models’ fuel efficiency — their gas mileage — and Ford was forced to roll back its efficiency claims. Improved fuel efficiency — spewing less carbon dioxide — is key to fighting global warming.

Among the testing flaws: The protocol lets companies routinely measure their most efficient, least polluting models and then extrapolate across their entire production, projecting companywide mileage to demonstrate whether they are meeting government standards. This allows them to deliver the most optimistic, though not necessarily accurate, reports. And you wonder why the mileage you get differs from what the window sticker claimed?

Rather than spot-checking 15% to 20% of all models before allowing companies to offer them for sale, the government must check 100% — on the road as well as in the lab. The automakers’ cheating has made the expanded testing necessary. They must pony up the additional cost.

EPA must also find out which VW officials were responsible for what appears to be one of the biggest frauds in recent automotive history and how the company will make sure that every polluting vehicle is repaired.

Agency hearings featuring sworn testimony from all auto CEOs — subject to perjury laws — should explore whether their vehicles pollute too much. The lasting image of Big Tobacco’s chiefs lined up to tell congressional investigators 20 years ago that nicotine is not addictive might make the auto executives think twice about similar deception.

Clearly, the penalties haven’t been sufficient to discourage cheating.

The government must levy the strongest allowed punishment on VW. Anything less than roughly $18 billion — reflecting the maximum allowable fine of $37,500 per vehicle — would be inexcusable.

The threat of criminal prosecution of company executives could be an even more powerful disincentive to fraud. The administration must prosecute any VW officials who helped the company break the law, and it must be prepared to go after executives at other companies found to be getting around emissions requirements.

The automakers have a long history of fighting environmental proposals and lobbying for loopholes. No environmental victory is safe from this errant industry. Car makers are now trying to weaken the Obama administration’s fuel efficiency standard that would deliver a new-car fleet averaging 54.5 mpg in 2025 — arguably the biggest single step any nation has taken to fight global warming.

Volkswagen’s conduct is only the latest evidence that auto companies cannot be trusted to implement critical laws that keep the air clean and fight global warming pollution. Only strict regulation will do the job. We need tight monitoring by regulators with strong enforcement authority and the guts to make sure companies comply with strict regulations, and an auto industry that is certain it will face painful punishment if caught.

Government guard dogs must watch more closely and bark louder. But that's not enough; auto companies must feel their bite as well.